Abstract
The development of short-wavelength nonlinear optical (NLO) materials is indispensable and urgently required for further applications. Halides have been disregarded as potential NLO materials with deep-ultraviolet (DUV) cutoff edges due to their weak second-harmonic generation (SHG) response and poor birefringence. Here, two novel and isostructural halides, KBa(3)M(2)F(14)Cl (M = Zr (KBZFC), Hf (KBHFC)), possess structures that are formed by isolated MF(7) monocapped triangular prisms and dissociative K(+), Ba(2+), and Cl(-) ions. Compared with reported metal halides that are transparent to the DUV region, KBZFC and KBHFC possess the strongest SHG responses (approximately 1, 0.9 × KH(2)PO(4)), which are contributed by the synergistic effect of MF(7) (M = Zr, Hf) groups, Ba(2+) cations, and Cl(-) ions. The zero-dimensional structures favour sufficient birefringences (0.12, 0.10 @ 1064 nm) for phase-matchable (PM) behaviours. The discovery of KBZFC and KBHFC showcases the potential of NLO mixed metal halides transparent to the DUV region.